1. Field of the Invention
This invention relates to the art of printing, and, more particularly, to an apparatus and method for belt transfer printing of inked patterns onto nonflat surfaces of porous workpieces.
2. The Prior Art
It is often desired to print a design on the surface of a workpiece. Difficulties may arise when the workpiece surface to be printed includes significant nonplanar regions. An example of such a workpiece is a molded hardboard doorskin such as is manufactured and sold by the Masonite Corporation under the trademark "Colonist". This doorskin has much of its surface significantly recessed and embossed to simulate the form and texture of natural wood architectural millwork. The simulation may be further enhanced by printing the surface of the doorskin with a wood grain pattern. The pattern must be properly registered with the workpiece to correspond with the three-dimensional features of the workpiece.
Conventional printing devices such as press platens and gravure cylinders will generally be incapable of conforming and printing to a nonflat surface. Prior art methods of printing to such surfaces include use of an elastic transfer member. For example, U.S. Pat. No. 2,904,916 discloses a printing apparatus wherein a design is first screened onto a rubber transfer mat. The workpiece, of a porous material, is placed in a support. The mat is sealed over the workpiece and vacuum produced through the support draws the mat into contact with the workpiece, thus transferring the design to the workpiece surface.
In U.S. Pat. No. 2,202,465 there is disclosed a printing apparatus wherein the transfer member is an endless elastic belt. An inked plate is positioned below the belt, then the belt is momentarily pressed against the plate. The plate is then removed. A nonflat workpiece is positioned below the belt, then the belt is pressed into contact with the workpiece by pressure from above. After printing of the workpiece, the belt is advanced through a cleaning bath.
In these and other approaches of the prior art in which a transfer member is used to print a registered pattern on a three dimensional workpiece, the inking of the transfer member and the printing of the workpiece are sequential steps. That is, while the transfer member is receiving the pattern it is unavailable for printing to the workpiece, and vice versa. The throughput of such approaches is therefore significantly limited by the necessity of waiting for the inking of the transfer member before the workpiece can be printed.
What has been lacking is an apparatus and method for registered transfer printing wherein the transfer member is simultaneously available for receiving a pattern and for printing the pattern to the workpiece.